1. Field of the Invention
This invention relates in general to chairs for supporting reinforcement bars or wire mesh at a pre-selected elevated position above a bearing surface during the formation of a concrete slab, and more particularly to non-rigid chairs that are compressible when receiving a predetermined minimum load and resilient to return to their original shape when the load is reduced below the predetermined minimum load.
2. Prior Art
Concrete and many plastic compositions have a relative weak tensile strength. When used to form a slab these compositions will be placed in tensile stress from imposed loads, thermally induced changes or solidification upon setting. To increase the tensile strength of the slab, reinforcing wire fabrics, rigid metal bars, grids formed by relatively thin wire compression welded to one another at their points of intersection, and frameworks are employed as skeletal reinforcing members.
It is generally the practice to lay out or form a rigid iron framework or intersecting wire grid and then to pour the wet concrete over the grid. Upon the setting of the concrete a slab construction is completed. A proper slab construction presupposes that the grid is properly positioned within the slab. For best results, the grid should be positioned where the greatest protection from stress is needed. This is generally close to the surface of the concrete. However, after the concrete has set the grid should be completely covered by the concrete to avoid corrosion of the grid.
It is often the practice in such constructions to position a grid a few inches above the ground by resting the grid upon rigid supports or chairs. However, in actual practice the grids do not remain in their initially arranged pre-selected positions. For example, workers often walk upon the grid during the pouring operation. This can result in the chairs being rotated or otherwise forced off the grid. To prevent this from occurring most chairs used are designed to affix to the grid wire at the points of intersection. Examples of such rigid chairs are illustrated in U.S. Pat. No. 3,255,565 entitled “Reinforcement Spacer” and issued to A. Menzel on Jun. 14, 1966, U.S. Pat. No. 3,471,987 entitled “Positioning, Spacing and Supporting Device” and issued to D. F. Yelsma on Oct. 14, 1969, U.S. Pat. No. 3,673,753 entitled “Support Device for Concrete Reinforcing Bars” and issued to George C. Anderson on Jul. 4, 1972, U.S. Pat. No. 3,693,310 entitled “Support for Elongated Reinforcing Members in Concrete Structures” and issued to Thomas E. Middleton on Sep. 26, 1972, U.S. Pat. No. 3,830,032 entitled “Mesh Chair for Concrete Reinforcement” and issued to Wayne F. Robb on Aug. 20, 1974, U.S. Pat. No. 5,107,654 entitled “Foundation Reinforcement Chairs” and issued to Nicola Leonardis on Apr. 28, 1992, U.S. Pat. No. 5,555,693 entitled “Chair for Use in Construction” and issued to Felix L. Sorkin on Sep. 17, 1996, and U.S. Pat. No. 6,276,108 entitled “Device for Supporting and Connecting Reinforcing Elements for Concrete Structures and issued to John Padrun on Aug. 21, 2001.
While these rigid chairs improved the maintenance of connection with the grid, the rigidity of chairs in many cases caused wire forming the wire mesh to bend and create uneven areas in the surface of the grid. In attempts to at least partially remedy such defects workers sometimes try to pull the grid upwardly back into position or straighten the grid before the concrete has set. Such efforts are generally only partially successful at best. In order to overcome this problem chairs were constructed to be compressible when the wire mesh was pressed down on the chair by workers walking on the grid, but to also be resilient to reform its original shape when the load was removed from the chair. Examples of this compressible, resilient chair are disclosed in U.S. Pat. No. 3,368,320 entitled “Reinforcing Bar and Frame Supports” and issued to applicant on Feb. 13, 1968. These designs have evolved to the current Mesh-ups® chairs sold by John L. Lowery & Associates, Inc. doing business as Lotel, and owned by applicant.
One problem with the compressible, resilient chair has been the separation of the support legs from the setting resulting from repeated compression-recovery forces. Because of the varying depth of slabs it is common for the chairs to come in different sizes. As the chairs become larger they become more expensive in large part due to the increased plastic material needed to construct the chair. Therefore, it would also be desirable to construct a chair having the required compression and resiliency characteristics, but which required the use of less plastic material in the construction. Additionally, although these compressible, resilient chairs do grip the wire mesh when a load is applied to the grid it is desirable to have a chair that improves the gripping action of the chair prongs to the intersecting sections of wire to minimize the risk that a chair will become disengaged from the wire mesh by the cantilevering force resulting from stepping on the wire grid.